The present invention relates to industrial fasteners and more particularly to nut plates.
At the present time a number of industrial fasteners are available which act like a nut in retaining a screw. Such fasteners, when formed from sheet metal, are often called "nut plates", since they retain a screw and act as a plate in distributing the load. Such nut plates are frequently employed as reinforcement members when the panel wall is relatively weak; for example, a panel may be formed of thin plastic or thin metal. In certain refrigerators, the inner wall, called a liner, is of plastic, the outer wall is of metal or plastic, and the space between them is filled with a foamed-in-place insulation. The nut plate is positioned in a pre-formed hole in the liner. The nut plate must include a means of sealing the hole so that foam does not escape through the hole during the foaming of the insulation.
It is important that the nut plate not rotate ("a spinner") or collapse when the screw is first applied or when it is tightened. The primary means of preventing spinners is the adhesive holding the nut plate to the panel. But even if the nut plate is prevented from spinning, it may fail when the screw is tightened. If excess torque is applied to the screw, the dome forming the screw impression may collapse. Since the screws are applied after the foaming of the insulation, making the nut plate generally inaccessible, the failure of the nut plate due to such dome collapse is a serious problem.
It is known, from prior patents and commercially available devices, to secure a screw or other fastener using a plate held against the inside of a wall. In Krueger U.S. Pat. No. 3,298,271 a nut plate consists, in one embodiment, of a sheet metal plate having a screw hole and a projecting tab. A double-sided foam tape, having pressure sensitive adhesive on its faces, is adhered to the bottom face of the plate and a tab from the plate projects through the tape. In Ryder U.S. Pat. No. 3,747,657 a plastic nut-plate fastener, for the plastic wall of a foamed-in-place insulation refrigerator, has a plastic body with double-sided adhesive tape. In Hoadley U.S. Pat. No. 3,802,476, also for use in a foamed-in-place refrigerator, a metal plate has a central helical screw impression, a pair of tabs and a pair of wings at opposite ends of the plate. The face of the plate is covered by a double-sided foam tape. In Knowlton, also for use in a foamed-in-place refrigerator, a metal member has a top leaf, called an "upper plate", with a screw impression; a "U" shaped connecting portion; a pair of projecting tabs ("arms") and a bottom leaf ("base"). The top leaf and bottom leaf are pressed together when the fastener is manufactured.